Variable a.c. transducer



R. A. M MILLAN VARIABLE TRANSDUCER June 12, 1962 3,039,043

Filed May 5, 1959 IN VEN TOR.

264mm AMAWLM United States Patent 3,039,043 VAREABJLE A.C. TRANSDUCERRaymond A. MacMillan, Greenwood, Mass., assignor to the United States ofAmerica as represented by the Secretary of the Air Force Filed May 5,1959, Ser. No. 811,237

4 Claims. (Cl. 323-66) (Granted under Title 35, [1.5. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the United States Government for governmental purposes withoutpayment to me of any royalty thereon.

This invention relates to a circuit for controlling large alternatingcurrent signals, and more particularly a circuit wherein a directcurrent potential is utilized to control aforesaid alternating currentsignals.

In accordance with the present invention, a novel circuit is providedthat varies the apparent A.C. resistance of aforesaid current from a fewohms to several megohms. The apparent A.C. resistance is automaticallycontrolled by a direct current potential. In addition to the foregoingfeatures, an AC. signal may be modulated by applying a proper D.C.modulating potential in place of the D.C. control potential.

An object of the present invention is to provide a novel circuitresponsive to a D.C. potential for controlling alternating signals.

Yet another object of the present invention is to provide a novelcircuit wherein a smooth control of an alternating current signal isobtained in response to a direct current potential.

Still another object of the present invention is to provide a novelcircuit wherein an apparent'alternating current resistance is controlledin response to a direct current potential.

A further object of the present invention is to provide a unique circuitwherein an alternating current signal is modulated by a varying directcurrent potential.

Further objects, features and advantages of this invention will suggestthemselves to those skilled in the art and will become apparent from thefollowing description of the invention taken in connection with theaccompanying drawing.

In the single figure of the drawing, there is shown transformer 1 havinga single ended primary Winding and a center tapped secondary winding.The primary winding is adapted to receive an alteranting current signalat terminals 2. The center tapped secondary Winding has terminals 3, '4,and 5. Full wave dry rectifier bridge 6 is supplied at point 8 with analternating signal from terminal 3 by way of adjustable resistor 7 andat terminal 9 directly from terminal 5. The alternating current signalat terminal 8 is 180 out of phase with that at point 9. Positiveterminal 10 of rectifier bridge 6 is connected to anode 13 of electrondischarge device 12. Negative terminal 11 of rectifier bridge 6 isconnected to cathode 14 of electron discharge device 12. Control grid 15of electron discharge device 12 is returned to cathode 14 by way ofresistor 16.

An alternating current flows from center tapped terminal 4 oftransformer 1 through external load 21 by way of output terminal 19 andthen to output terminal 2%. Load 21 may be any external circuit ordevice being supplied an alternating current signal being controlled bya D.C. potential. From output terminal 20, the alternating current flowsthrough rectifier bridge 6 by way of terminal 8 and terminal 9 andthence to terminal of transformer 1.

The magnitude of the aforementioned alternating current is primarilydetermined by the unbiased resistance 3,039,043 Patented June 12, 1962"ice of electron discharge device 12. In the normal operation ofelectron discharge devices complete cutoff is not obtained and a smallresidual current would flow. Under this condition, a current of oppositephase is applied to rectifier bridge 6 from terminal 3 of transformer 1by way of adjustable resistor 7. By adjusting the value of resistor 7,current in external load 21 can be made zero for approximate cut-off ofelectron discharge dew'ce 12. With the aforesaid approximate cut-offexisting in electron discharge device 12, currents of a small magnitudecontinue to flow so that the aforesaid adjusting of the value ofresistor 7 permits the voltage drop thereacross to be equal to thevoltage drop across terminals 8 and 9 of rectifier bridge 6 and hencethere can be no current flow in .load 21. The negative potentialnecessary to control electron discharge device 12 may be applied toterminals 17 and 18, obviously any value between full conduction andapproximate cut-off can be obtained by varying the D.C. controlpotential applied to terminals 17 and 18. The magnitude of thealternating current flow is then determined precisely and in directproportion to the magnitude of the D.C. potential applied to electrondischarge device 12 by way of terminals 17 and 18. Thus, there isprovided a precise control of relatively large alternating currentand/or power by means of a novel circuit responsive to D.C. potentials.

The phase of the alternating current signal at terminals 19 and 20 maybe 0 or 180 and is uniquely determined by the polarity of the D.C.control potential applied to electron discharge device 1 2 by way ofterminals 17 and 18, hence the circuit of the present invention alsoprovides a novel phase transducer.

There is also shown an output circuit having frequency selectivecharacteristics. The frequency selective circuit is comprised oftransformer 22, with its primary tuned to parallel resonance bycapacitor 23. The secondary of transformer 22 feeds a series resonantcircuit consisting of inductor 24 and capacitor 25. The preselectedfrequency is then available at output terminals 26 and 27.

The novel circuit of the present invention produces 1.5 volts R.M.S. for0.1 volt D.C. input. Power was volts 60 cps. other variations were alsoutilized, in one instance a 50 watt variation in power was controlled bya D.C. potential. Another application for the present invention residesin a compact and economical unit to use in place of large amplifiers tocontrol large power at line frequencies.

What is claimed is:

1. Apparatus to control alternating current signals comprising atransformer adapted to receive said alternating current signals, saidtransformer having a center tapped secondary with two outer legs, a fullwave bridge rectifier having a pair of alternating current inputterminals, and a pair of direct current terminals, an outer leg of saidsecondary winding being connected to one of said pair of alternatingcurrent input terminals by way of an adjustable resistor, the otherouter leg being connected to the other of said pair of alternatingcurrent input terminals, an electron discharge device having an anode,cathode and control grid, said pair of direct current terminals of saidrectifier being connected across said anode and said cathode of saidelectron discharge device, means to control the rate of conduction ofsaid electron discharge device, and a pair of output terminals for saidcontrolled alternating current signal, one of said output terminalsbeing the center tap of said secondary winding and the other being .oneof said terminals said alternating current input terminals.

2. Apparatus to control the rate of flow of alternating current signalscomprising a transformer receiving said alternating current signals,said transformer having a center tapped secondary winding, a full waverectifying bridge having two alternating current input terminals saidtwo terminals being connected across said secondary winding by way ofalternating current signal adjusting means, means connected in thedirect current path of said full wave bridge rectifier to control thecurrent flow therein, said current flow control means receiving a directcurrent control potential, and an output circuit for said alternatingcurrent signals, said output circuit including said center tap of saidsecondary winding and one of said two alternating current signal inputterminals.

3. Apparatus to control the rate of flow of alternating current signalscomprising a transformer adapted to receive said alternating currentsignals, said transformer having a center tapped secondary winding, afull wave bridge rectifier having two alternating current inputterminals, said tWo terminals being connected across said secondarywinding by way of alternating current signal adjusting means, anelectron discharge device connected in the direct current path of saidfull wave bridge rectifier, means to apply a direct current potential tosaid electron discharge device to control the rate of conductionthereof, and an output circuit for said alternating current signals,said output circuit including said center tap of said secondary windingand one of said two alternating current signal input terminals.

4. Apparatus for controlling alternating current signals comprising atransformer adapted to receive said alternating current signals, saidtransformer having a center tapped secondary winding, a full wave bridgerectifier having tWo alternating current signal input terminals and apair of direct current output terminals, said secondary winding beingconnected across said pair of input terminals by way of alternatingcurrent signal adjusting means, an electron discharge device having ananode, cathode and control grid, said pair of direct current outputterminals being connected across said anode and cathode of said electrondischarge device, means to apply a direct current potential to saidcontrol grid of said electron discharge device to control the rate ofconduction thereof, a pair output terminals for said controlledalternating current signal, said output terminals being said center tapof said secondary winding and one of said two input terminals.

Trucksess -a Nov. 6, 1951 Shrider et al. Oct. 24, 1957

